Radiation therapy is the treatment of malignant tissue through the use of radiation. The guiding principle is that malignant tissue has diminished ability to repair the radiation damage; whereas normal, healthy tissue retains the ability to recover from radiation exposure. Therefore, if a tumor is exposed repeatedly to radiation, it should shrink in size or disappear and, as long as the neighboring healthy tissue is given adequate time to recover between treatments, there should not be excessive permanent damage.
The goal of radiation therapy is to deliver the radiation to the tumor itself while minimizing exposure of surrounding normal, healthy tissue. One important step in this process is treatment planning. Fractionated treatment, i.e. treatment involving the division of total radiation dose into twenty or thirty subparts, has been used for decades in an effort to maximize recovery time for healthy tissue, as well as to minimize side effects and complications from overexposure to radiation. Stereotactic techniques have been developed which employ accurate positioning of the patient during radiographic studies so as to improve the precision in locating tumors and the delivery of radiation. Over the years, the use of radiographic devices such as x-rays and CT scanners in this process has become common, and now the use of Magnetic Resonance Imagery technology (MRI) is being actively investigated. These imaging techniques enable the radiation oncologist to look inside the body and avoid invasive surgery which might otherwise be necessary to locate and describe the lesions.
The development of treatment planning systems has been rapidly evolving. The x-ray pictures produced by traditional simulators provide the physician with a "beam's-eye view" of a tumor within a patient. This technology had the disadvantage that it helps to visualize only hard structures within the body, such as bones, but would not provide accurate and clear pictures of soft tissues, i.e. tumors or sensitive organs.
Following the development of the Computerized Tomography or CAT-scan technology, a computer simulator program was developed which is able to produce three-dimensional images showing soft tissue and tumor structures. This technology represented a great advance over the prior art, but it has been slowly adopted because of three major drawbacks. First, to develop the three-dimensional images to depict the tumor and other sensitive organs, a technician must abstract information from CT scans slice by slice, which is very time-consuming. Second, because of the abstraction process, one loses much of the anatomy that is desirable in preparing a treatment plan. Finally, this technology has the disadvantage that the dosing curves that are superimposed online drawings of the anatomy are very difficult for the physician to interpret.
In radiation oncology, it has long been important to immobilize the patient during treatment and radiographic examination in order to assure that radiation is delivered exactly where it is needed and that tumors and surrounding normal structures are precisely located. Existing immobilization systems, however, have proven incompatible with MRI-based techniques. Because of the size limitations of the MRI magnetic head coil, it is virtually impossible to utilize a standard immobilization system. In addition, the presence of the stainless steel structures present in classic stereotactic immobilization systems cause severe distortion of the MRI image.
A three-dimensional treatment planning software product has been developed by George Sheroure, Phd. under the name of Gratis. This software includes a program called Virtual Simulator which takes information abstracted from CT scans and develops three-dimensional images. This is strictly for CT scans and there is no suggestion of applying the program to or MRI technology.